The present invention relates to multiwavelength routers for use in Wavelength Division Multiplexed (WDM) systems and, more particularly, to widening the passbands of a WDM using a combination of two gratings of opposite angular dispersion.
Optical networks require efficient wavelength routers with minimal loss and maximum passband width. A wide passband for the router transmission coefficients is desirable because it reduces the need for accurate control of the transmitted wavelengths. It is also needed in channel adding/dropping filters, which must be designed with a maximally flat response, if many routers have to be concatenated. Often, each router is realized in integrated form as in reference [1], by using an imaging arrangement of waveguides (arms) having a constant path-length difference. (in this specification, a reference is designated by a number in brackets to identify its location in a list of references found in the Appendix) It is then possible to cause each transmission coefficient to approach a rectangular response by concatenating two integrated routers as shown in references [2-4]. This arrangement is suitable for integration on a single wafer, provided the number of ports is not too large. However, a limitation of that arrangement is the large size of the two waveguide gratings which makes it difficult to realize a wavelength router arrangement on a single wafer.
What is desired is a multiwavelength router having an increased number of wavelength channels with widened passbands.
In accordance with my invention, the passband of an optical wavelength router is widened by using a combination of two grating apparatuses with opposite angular dispersions. The passband width approaches the channel spacing, with minimal loss penalty. This technique is particularly attractive for applications requiring a large number of ports with maximum passband width and relatively small loss.
More particularly, an optical wavelength router comprises an input optical link, an output optical link, and an imaging arrangement including two gratings of different orders having essentially equal but opposite dispersions chosen so that an input wavelength transmitted from the input optical link to the output optical link essentially produces at the output optical link receiving aperture a stationary image whose intensity variation as a function of input wavelength produces a passband that is primarily determined by a transmission coefficient of the grating of higher order.
According to other aspects of our invention, the optical wavelength router may be formed using either reflective or transmissive elements formed using grating apparatuses that include free space optical elements or waveguide gratings. The optical wavelength router can be used as an optical signal multiplexer or demultiplexer.
My method of demultiplexing a wavelength division multiplexed (WDM) signal comprises the steps of: (1) receiving a WDM signal, forming therefrom an incident plane wave, and distributing it, (2) transforming a received incident plane wave into a set of planes waves of different orders having a first dispersion value, and (3) diffracting the set of plane waves with a second dispersion value essentially equal to and opposite of the first dispersion value and forming therefrom different wavelength signal of the WDM signal.
My method of multiplexing a plurality of wavelength signals into a wavelength division multiplexed (WDM) signal comprises the steps of: (1) transforming each of the plurality of wavelength signals into a set of planes waves having a first dispersion value and distributing the set of planes waves, and (2) diffracting the set of plane waves with a second dispersion value essentially equal to and opposite of the first dispersion value and forming therefrom the WDM signal.